We haven't used MightySites, so I can't answer specifically. I think you may run into some issues with multiple domains with some of the social networks though. Facebook does allow you to add multiple domains in their configuration area, along with multiple callback URLs. However, other networks only allow one URL or domain to be used, which would prevent those social networks from authenticating on the additional domains.
In general though, I'd have to simply say to try it and see what happens as I can't think through all the issues you may run into and if they'd be solvable until we hear what they may be.
A lot of functionality, like social buttons, should just work though.
I hope that helps get you started with some ideas of where to focus on possible issues.
Thanks,
Alex
Multi Site Environment - Possible ? Need to Know!
